Matt Kaeberlein/FUSION

All dogs go to heaven—but maybe they don't have to. Scientist Matt Kaeberlein thinks he may have discovered a cure for canine aging.

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Kaeberlein, a biologist at the University of Washington, has been conducting experiments for decades that explore how factors like genetics and calorie consumption affect how we age, and whether there are drugs that might be able to slow the process. This year he and a colleague, Daniel Promislow, began a clinical trial to test whether a drug called rapamycin that has been known to increase the lifespan of mice might do the same for dogs; he says the results of a preliminary study are astonishing. And he's already thinking about what it could mean to give the drug to the dogs' owners.

"I was shocked when I got the data," he said. "It is almost certain that rapamycin can slow the effects of aging in dogs and people. The only question is whether it can slow aging with doses that don't have significant side effects."

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Kaeberlein, a dog lovers with two pooches of his own, wanted to use people's pet dogs to study aging for a few reasons. For one, dogs are a great proxy for human research: the conditions in which dogs live are much closer to our own than the lives of laboratory mice. Dogs also age much faster than we do—the average lifespan of a dog is just 10 to 13 years—meaning that scientists can study the entire aging process in just a few short years. Plus, helping dogs live longer benefits their human owners, too.

"If we can delay aging in people’s pets," he told me, "it will directly improve their quality of life at the same time that it provides insight into human aging."

In his initial experiment, which concluded in March, 40 people gave their dogs tablets of rapamycin three times a week. Kaeberlein then took several echocardiograms of the dogs over a 10-week period to determine the effect of the drug on heart function.

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Rapamycin is an immunosuppressive drug that acts like a volume knob for what's known as the mTOR pathway, which regulates cellular signals including cellular growth. The presence of rapamycin can help slow cell aging, interfering with the ability of the mTOR pathway's ability to pick up on those signals that cause cells to grow; the more rapamycin is present, theoretically, the more signal interference. The drug is frequently used in transplant patients, to help prevent an organ's rejection, and to stem the growth of certain types of cancer.

Kaeberlein's initial trial tested low doses of the drug on large, middle-aged dogs, to ensure that it didn't do long-term damage. After some dogs were weeded out for heart conditions and other factors, 24 dogs completed the double-blind trial. The results, which have yet to be published, found that the dogs that received the drug showed heart functionality that either improved or remained the same (in dogs, 10 weeks is enough time to potentially see some cardiac decline). The dogs that had come in with worse cardiac conditions seemed to improve the most.

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These results are promising, but preliminary—just 24 dogs is a small study, and the effects of rapamycin were only measured over a few weeks. But it suggests something promising: just like in mice, it seems rapamycin may indeed help dogs stay healthy longer. Kaeberlein now plans to run years-long trials on dogs. And he's hopeful rapamycin might even be approved for people by the next decade.

Kaeberlein isn't the only scientist wondering whether rapamycin might be a fountain of youth—it's one of the most promising anti-aging drugs currently being tested in labs. In 2009, researchers at the University of Texas showed it could extend the lives of older mice by between 9 and 14 percent. Subsequent studies found that rapamycin had similar effect on middle-aged mice, and that with higher doses that number could climb as high as 30 percent. In mice, it also seemed to slow age-related diseases such as cancer and Alzheimer’s.

In 2014, the drug company Novartis revealed that it had tested a compound derived from rapamycin on elderly humans and that it had successfully increased immune response to a flu vaccine by 20 percent. Like Kaeberlein's study, it was preliminary—the study only looked at immune response over a short period of time—but it also suggested rapamycin might eventually extend the lives of people, too.

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Many scientists in the aging field feel that if rapamycin can extend the lifespan of mice by up to 30 percent, it should be able to do the same for people, too. The question, Kaeberlein told me, is not so much whether rapamycin might help slow the aging process for humans, but whether you can do so without creating side effects that make living longer seem less worth it.

In rats, for example, rapamycin can cause infertility.

"You have to ask, is that a fair trade-off for an extra 15 percent of healthy longevity?" Kaeberlein said. "When we are talking about aging interventions, the tolerance for side effects is less. There’s a difference between quality and quantity of life and the goal is a balance of the two."

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There are other drugs out that that might also one day help us all live longer. Metformin, a diabetes drug that has also been shown to extend life in mice, will soon be tested in non-diabetic elderly people to see whether it might prevent age-related ailments such as cancer, stroke and dementia. Resveratrol, a compound found grapes and blueberries, is also being studied for its anti-aging benefits.

But Kaeberlein is most excited about rapamycin.

"Helping people's pets live longer will go a long ways toward convincing people that it should also be tried in humans," he told me. "Everything about biological science says that it should work the same in humans."